Purpose: The stability of ertapenem solution in syringes at room, refrigerator, and freezer temperatures was determined to establish options for extended storage.

Methods: Six replicate solutions of ertapenem (100 mg/mL) in 0.9% sodium chloride injection were prepared in 20-mL polypropylene syringes and stored at 25, 4, or −20 °C. Syringe samples were collected immediately after preparation and at preselected time points and assayed by a validated high-performance liquid chromatography (HPLC) method. The ertapenem solution was considered stable if at least 90% of the mean initial concentration remained at the time of HPLC analysis.

Results: The mean ± S.D. baseline ertapenem concentration across all stability studies was 109.9 ± 9.2 mg/mL. One hour after preparation, the mean ± S.D. ertapenem concentration of samples kept at room temperature was 87.8 ± 4.6% of the initial concentration. After 24 and 48 hours of refrigeration, mean ± S.D. drug concentrations had declined to 93.6 ± 5.9% and 86.2 ± 4.3% of the respective baseline concentrations. Frozen syringes required 1 hour to thaw at room temperature; after 14 and 28 days of frozen storage, the mean ± S.D. ertapenem concentrations of these samples 4 hours after thawing were 93.4 ± 3.5% and 86.4 ± 2.6% of the respective baseline values.

Conclusion: Ertapenem 100 mg/mL prepared in 20-mL polypropylene syringes was stable at room temperature for approximately 30 minutes. Room-temperature stability was extended to 4 hours after 24 hours of refrigeration. After being frozen for 14 or 28 days, ertapenem was stable for 3–5 hours after removal from the freezer.